Plants synthesize signaling molecules in response to wounding, herbivore attack and pathogen attack. These compounds are derived from linoleic acid and stimulate the expression of several genes referred to as jasmonate-induced proteins. These include proteinase inhibitors, thionins, vegetative storage proteins, lipoxygenases, ribosome-inactivating proteins, enzymes of phenylpropanoid metabolism, and others. The jasmonates can also repress the expression of genes related to photosynthesis at the transcriptional and translational levels.
Coronatine is a phytotoxin produced by several pathovars of Pseudomonas syringae which induces leaf chlorosis, inhibits root growth and is thought to play a role in disease development by suppressing the disease-resistance genes and mimicking the action of methyl jasmonate. The COI1 protein contains an F-box-like motif and leucine-rich repeats. This protein may recruit regulators of defense response and pollen development for modification by ubiquitination (Xie et al., “COI1: An Arabidopsis Gene Required for Jasmonate-Regulated Defense and Fertility”, (1998) Science 280:1091-1094).
The maize Lls1 (lethal leaf spot1) locus is characterized by the initiation of necrotic lesions which expand to kill leaf-cells autonomously. The Lls1 gene is required to limit the spread of cell death in mature leaves. The Lls1-encoded protein (LLS1) contains two consensus binding motifs of aromatic ring-hydroxylating dioxygenases and may function to degrade a phenolic mediator of cell death. The LLS1 protein is expressed predominantly in the leaf epidermal tissue (Simmons et al. (1998) Mol. Plant Microbe Interact. 11:1110-1118; Gray et al. (1997) Cell 89:25-31).
The sequences encoding COI1 from corn, rice, soybean and wheat have yet to be determined as are the sequences encoding rice, soybean and wheat LLS1. Manipulation of the COI1 or LLS1 genes will be useful in engineering broad spectrum disease, insect and stress resistance. The genes encoding LLS1 will also be useful for herbicide discovery and design.